The present invention relates to intraocular lenses, particularly to methods for attaching a haptic to an optic using laser welding.
Intraocular lenses have been known since about 1950. They are used to replace the natural lenses of eyes that have been damaged by trauma or disease, such as cataracts. A typical intraocular lens ("IOL") comprises an artificial lens ("optic") and at least one support member ("haptic") for positioning the IOL within the capsular bag of the eye. The optic may be formed from any of a number of different materials, including polymethylmethacrylate (PMMA) and acrylics, and it may be hard, relatively flexible or even fully deformable so that the IOL can be rolled or folded and inserted through a relatively small incision in the eye. The haptic generally is made of some resilient material, such as polypropylene or flexible copolymers of PMMA. IOL's may be characterized as either "one-piece" or "multi-piece." With one-piece IOL's, the haptic and the optic are formed integrally as a blank and the IOL is then milled or lathed to the desired shape and configuration. The multi-piece IOL's are formed either by attaching the haptic to a pre-formed optic or by molding the optic around an end of the haptic.
U.S. Pat. Nos. 4,834,751 and 4,894,062 (both to Knight, et al.) describe haptic attachment methods whereby the haptic and an anchoring member are joined and the optic is molded around the end of the haptic having the anchoring member. While these methods provide strong haptic-optic interlock, the procedure for molding an optic around the previously joined haptic and anchor member is complex and requires special care to maintain the haptic in place while the optic material is cured, and to remove the cured IOL from the mold without damaging the haptic.
Many methods for attaching a haptic to a pre-formed optic are known, including those involving the use of adhesives. If an adhesive is used to attach a haptic to an optic, the adhesive must be strong, biologically inert and resistant to degradation by bodily fluids. At present, there are few materials that satisfy all these requirements. In addition, there will always be a concern that the adhesive will deteriorate over time, resulting in loose or detached haptics within the eye.
Other more common methods for attaching a haptic to a pre-formed optic involve the use of heat. One such haptic attachment method involves drilling intersecting holes into the periphery of an optic and inserting one end of the haptic into one of the holes. A heated probe is inserted through the other hole, contacting the embedded end of the haptic and causing a portion of it to melt and flow laterally into the second hole. When the embedded haptic end cools and hardens, a mechanical interlock with the optic is formed. A similar method is disclosed in U.S. Pat. No. 4,104,339 (Fetz, et al.), where a haptic hole is made in the peripheral edge of an optic, the haptic end is inserted into the hole and then an inductively heated thin probe is pushed through the posterior face of the optic into contact with the haptic end to form a crimped connection between the haptic and the optic. This is currently the most common method used for attaching haptics to optics. However, this method damages the optic surface where the heated probe is pushed through to the haptic end and thus, compromises optical performance.
Another similar method is disclosed in U.S. Pat. No. 4,307,043 (Chase, et al.), where a hole having threaded recesses is made through a portion of the optic (the hole being essentially parallel to the plane of the optic) and one end of a haptic is inserted through the hole so that it projects beyond the optic. Heat is then applied to the haptic end projecting beyond the optic to melt a portion of it, which fills the threaded portions of the hole. When the haptic material hardens, a mechanical interlock with the optic is formed. This heat attachment technique is disadvantageous because skilled technicians and precise equipment alignment are required.
U.S. Pat. No. 4,786,445 (Portnoy, et al.) discloses another haptic attachment method which involves making a cavity having a shoulder in the periphery of an optic. The haptic end is inserted into the cavity and laser energy of a near infrared wavelength is transmitted through the optic to the haptic, causing the haptic end to melt and flow into the shoulder of the cavity. When the end hardens, a mechanical interlock between the haptic and the optic is formed. Although this method avoids some of the problems of the prior-mentioned methods, there are other disadvantages. Because the haptic end is melted to form a shoulder within the cavity of the optic, there is a likelihood of variation in haptic length, both between individual IOL's and between individual haptics attached to the same IOL.
U.S. Pat. No. 4,843,209 (Milligan) discloses a method of attaching a haptic to an optic using laser energy. However, the method disclosed uses a high-powered neodymium:yttrium-aluminum-garnet (Nd:YAG) laser that emits radiation in the non-visible spectrum, necessitating the use of a Helium-Neon (HeNe) aiming laser, and resulting in exacting Nd:YAG/HeNe laser alignment requirements. Furthermore, the method disclosed in this patent does not rely on a differential in laser energy absorption between the haptic and the optic to prevent optic damage (both the optic and the haptic being disclosed as comprising PMMA) and, instead, the disclosed method must carefully balance the amount of laser energy used with the time of exposure to insure that the optic is not damaged. The haptic absorbs the laser energy more readily than the optic because the optic has a smooth, flat surface while both the haptic and the hole in the optic contain a series of interlocking ridges that diffusion and deflect the radiation within the haptic This absorption method is inefficient, requiring the use of a relatively high laser power level (on the order of 50 watts) and is unnecessarily complex and expensive because of the difficulty in forming the ridges in the hole and on the haptic.
Accordingly, a need has continued to exist for a simple, reliable method of attaching a haptic to an optic of an intraocular lens without damaging the optic or otherwise distorting the optical properties of the optic.